Hydrogen Sulfide

The “rotten egg” odor that people complain about in well water can come from many sources, but it is most commonly caused by “sulfur reducing” bacteria that give off a foul-smelling gas. The bacteria themselves are harmless–they don’t cause disease–but the gas they produce can cause horrible odors and smelly black staining in pipes and appliances.

In some parts of the country, most notably Florida, where hydrogen sulfide is common and very severe, the standard treatment is to spray the water into an open air tank, allow the noxious gas to escape into the atmosphere, then use a secondary pump to send the water from the tank into the home. Tanks of this type are expensive, need lots of space, and are subject to freezing in cooler climates. Therefore, another type of treatment known as “precipitation/filtration” is preferred in most areas.

With this method, an “oxidizer” causes the trapped hydrogen sulfide gas to “precipitate” to elemental sulfur, then the sulfur is trapped in a filter. It’s a two-step process. The filter is most often carbon. Filter carbon, especially a specialty carbon called “catalytic carbon,” can perform both steps–precipitation and filtration–but unless the amount of H2S (hydrogen sulfide) is small, the carbon wears out quickly and has to be replaced. However, when the carbon is helped by a more powerful “oxidizer,” the carbon can last a very long time and the process can be very successful. Many “oxidizers” can cause the precipitation of the gas: air, chlorine, hydrogen peroxide, potassium permanganate, ozone, and more. For residential users, the most practical and the most easily maintained are aeration (air) and chlorination.

A full treatment system with chlorine looks like this–

1. A dry pellet chlorinator — a device that drops chlorine pellets into the well itself– followed by a carbon filter, or

2. A chemical feed pump, installed before the pressure tank, that feeds liquid chlorine (household bleach) into the water line. After the pressure tank, you must have a retention tank–usually 80 to 120 gallons–to give the chlorine time to work. After the retention tank, a carbon filter.

A full treatment system with aeration looks like this —

1. An “Aer-Max” system, which consists of a 10″ X 54″ treatment tank that is fed by a small air compressor. It is installed after the pressure tank, and it is followed by a carbon filter, or

2. A “single tank aerator” installed after the pressure tank. It is a backwashing filter with a special control valve that draws in air to “oxidize” the H2S so that it can be removed by the filter carbon in the bottom 2/3 of the tank.

Here are page links that show the various strategies. Many have installation diagrams.

The carbon filter used in any of these system (other than the single tank aerator) can be either a “backwashing” tank-style filter or a carbon block filter. If iron is present in the water, a backwashing filter must be used because a carbon block filter would be clogged quickly with iron.

Catalytic carbon is the carbon of choice with hydrogen sulfide, but any good carbon filter will work after proper oxidation.